$8de + 10df + 7d + 10 = 7e + 5$ Solve for $d$.
Solution: Combine constant terms on the right. $8de + 10df + 7d + {10} = 7e + {5}$ $8de + 10df + 7d = 7e - {5}$ Notice that all the terms on the left-hand side of the equation have $d$ in them. $8{d}e + 10{d}f + 7{d} = 7e - 5$ Factor out the $d$ ${d} \cdot \left( 8e + 10f + 7 \right) = 7e - 5$ Isolate the $d$ $d \cdot \left( {8e + 10f + 7} \right) = 7e - 5$ $d = \dfrac{ 7e - 5 }{ {8e + 10f + 7} }$